Bis[N,N′‑diisopropylbenzamidinato(−)]silicon(II): Cycloaddition Reactions with Organic 1,3-Dienes and 1,2-Diketones

Reaction of the donor-stabilized silylene 1 (which is three-coordinate in the solid state and four-coordinate in solution) with organic 1,3-dienes (2,3-dimethyl-1,3-butadiene, 1,3-butadiene, (E,E)-1,4-diphenyl-1,3-butadiene, 2,3-dibenzyl-1,3-butadiene, 1,3-cyclohexadiene, or cyclo­octatetraene) and 1,2-diketones (3,5-di-tert-butyl-1,2-benzoquinone or 1,2-diphenyl­ethane-1,2-dione) leads to the formation of the respective cycloaddition products 2–9. Compounds 2–9 were characterized by crystal structure analyses (7 was studied as the hemi solvate 7·​0.5n-C6H14) and NMR spectroscopic studies in the solid state and in solution. As the amidinato ligands can switch between a monodentate and bidentate coordination mode, for some of the cycloaddition products studied, the silicon coordination number in the solid state and in solution is different. For example, compound 4 is four- (4a) and six-coordinate (4b) in the solid state (isolated as a 1:1 cocrystallizate of 4a and 4b) and five-coordinate in solution. As demonstrated for the methanolysis of 2 (formation of 10; proof of principle), compounds 2–7 with their reactive Si–N bonds are starting materials for the synthesis of promising mono- and bicyclic organosilicon compounds.